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Introduction
Published in A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha, Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha
A voxel (volume element) is a 3D structure with known length, width and depth (a pixel with ‘depth’). Voxel geometry is important when reconstructing or manipulating images: voxels can be cuboidal in shape where all sides are equal in size – known as isotropic voxels (Fig. 1.17b) – or directional (where not all sides are of equal length) – known as anisotropic voxels (Fig. 1.17c).
Image in Multimedia
Published in Sreeparna Banerjee, Elements of Multimedia, 2019
An image is a spatial representation of an object or a two-dimensional (2D) or three-dimensional (3D) scene. A picture, which is a representation of a momentary event from a 3D spatial world, is an example of a 2D image, whereas a computer game can be a sequence of 3D images [1–7]. An image is modeled as a continuous function defining a rectangular region in a plane. Images formed from actual convergence of light rays are real images, whereas images formed from the extrapolation of light rays that are non-existent are imaginary. The image intensity distribution is proportional to the radiant energy received in the electromagnetic band to which the sensor/detector is sensitive (sometimes referred to as the intensity image) [1,2,6]. A digital image is represented by a matrix of numeric values, each representing a quantized intensity value I (r, c), where r is the row and c is the column. An image can be obtained in digital form by sampling the image intensity function at discrete intervals. The sample points representing the smallest discrete intensity value is called a pixel. A pixel [1–6] is essentially a picture element (pel) in two dimensions. A voxel is a 3D picture element of a very thin slice, or a volume element. This process of selecting the discrete points is referred to as sampling. The value of the intensity at each pixel is obtained by approximating the continuous value to a bin value. This approximation is referred to as quantization, and the approximation corresponds to the number of bits per pixel required to obtain this intensity value.
Assessing rechargeable batteries with 3D X-ray microscopy, computed tomography, and nanotomography
Published in Nondestructive Testing and Evaluation, 2022
Herminso Villarraga-Gómez, Dana L. Begun, Pradeep Bhattad, Kai Mo, Mansoureh Norouzi Rad, Robin T. White, Stephen T. Kelly
For each of the 3D X-ray imaging techniques presented above, the output data is a three-dimensional greyscale image composed of voxels representing the X-ray absorption in the 3D volume elements located in the battery. A voxel is the smallest volume element used for sampling the data into discrete entry units addressable/controllable in a 3D digital image, which is stored in computer memory as a numeric representation of intensity or grey level output from three-dimensional functions fed as input by spatial coordinates; it represents a ‘3D pixel’ in the volumetric data set [17,18]. The greyscale distribution is largely related to the density of the material that makes up the battery. The image may contain the entire battery or battery material sample, or a sub-volume of the sample. Volumes at different locations or resolutions obtained from the same instrument contain coordinate information that ensures they align well with each other when viewed in three-dimensional image visualisation and analysis software. Images from different instruments (e.g. X-ray CT and 3D XRM) can be aligned with each other using an image registration step to enable co-visualisation, see Figure 5. Segmentation algorithms can be used to identify different layer components in a battery and separate them by assigning false colours to cathode, anode, and aluminium and copper collectors. Commercial and open-source software packages are available to address these needs.
Isosurface rendering of medical images improved by automatic texture mapping
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2018
Thiago F. de Moraes, Paulo H. J. Amorim, Jorge V. L. da Silva, Helio Pedrini
Volumetric data sets are typically represented by a finite number of 2D cross-sectional slices. A volume element (voxel) corresponds to a position in the data set and stores a sampled value. The set of all these data values is known as a scalar field on the volume.